The present invention relates to an apparatus for loading a tubular graft, such as a stent, onto the distal end of a catheter assembly of the kind used, for example, in percutaneous transluminal coronary angioplasty (PTCA) or percutaneous transluminal angioplasty (PTA) procedures.
Prior art stents typically fall into two general categories of construction. A first type of stent is expandable upon application of a controlled force, for example, through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the compressed stent to a larger diameter to be left in place within the artery at the target site. A second type of stent is a self-expanding stent formed from, for example, shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. Such stents manufactured from expandable heat sensitive materials allow for phase transformations of the material to occur, resulting in the expansion and contraction of the stent.
Generally, in typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through the brachial or femoral arteries and advanced through the vasculature until the distal end of the guiding catheter is in the ostium. A guide wire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guide wire sliding within the dilatation catheter. The guide wire is first advanced out of the guiding catheter into the patient""s coronary vasculature and the dilatation catheter is advanced over the previously advanced guide wire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, a flexible and expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient""s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
In angioplasty procedures of the kind referenced above, restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the development of restenosis and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery at the lesion. The stent is transported through the patient""s vasculature to the implant site where it is to be deployed. At the implant site, the stent is expanded to a larger diameter. For a self-expanding sent, deployment is achieved by allowing the stent to be released from a delivery catheter where upon freedom from the constraints of the delivery catheter the stent self-expands. Alternatively for a balloon expandable stent, deployment is achieved by inflating a balloon portion of a dilatation catheter forcing expansion of the stent.
Because the catheter and stent must travel through the patient""s vasculature, and possibly through the coronary arteries, the stent must have a small delivery diameter and must be firmly secured within a delivery catheter until the physician is ready to implant it. Thus, the stent must be loaded onto the catheter so that it does not interfere with delivery, and it must not come off the catheter until it is implanted.
In procedures where a self-expanding stent is utilized, the stent is placed within a protective delivery sleeve of the delivery catheter. It is necessary to properly collapse the stent for loading into the protective delivery sleeve. This collapsing of the stent has proven to be a particular challenge where it is necessary to load the stent into a small diameter delivery catheter. Because of the inherent tendency for a self-expanding stent to resist compression, it is difficult to ensure a uniform collapse of the stent during the loading process without possible damage to or improper orientation of the stent. The resistance to compression is especially pronounced where it is necessary to load the stent into a small diameter delivery catheter because the stent must be collapsed down to an extremely small profile.
In procedures where a balloon expandable stent is utilized, the stent is placed over the balloon portion of the catheter, it is necessary to crimp the stent onto the balloon portion to reduce its diameter and to prevent it from sliding off the catheter when the catheter is advanced through the patient""s vasculature. Nonuniform crimping can result in sharp edges being formed along the now uneven surface of the crimped stent. Furthermore, non-uniform stent crimping may not achieve the desired minimal profile for the stent and catheter assembly. Where the stent is not reliably crimped onto the catheter, on rare occasions it is possible that the stent may slide off the catheter and into the patient""s vasculature prematurely as a loose foreign body, possibly causing blood clots in the vasculature, including thrombosis. Therefore, it is important to ensure the proper crimping of a stent onto the balloon portion of a catheter in a uniform and reliable manner.
It is generally the case that the collapsing or crimping of a stent is often done by hand, which can be unsatisfactory due to the uneven application of force resulting in non-uniform collapsing or crimps. In addition, it is difficult to visually judge when a uniform and reliable crimp has been applied.
As mentioned above, the problem often encountered with hand loading self-expanding stents into a delivery catheter is that given the natural tendency of self-expanding stents to expand back to an expanded profile. Upon compressing the stent for loading onto a catheter, the stent will quickly spring out of a compressed state thereby making it a cumbersome ordeal. Unlike balloon expandable stents that hug or grip the balloon in which the stent has been crimped, in order to successfully load a compressed self expanding stent a need exists for a collapsing device that will maintain the compressed state of the stent until it is successfully loaded within a protective delivery sleeve of a delivery catheter. Again, the difficulty in loading such a stent is increased where it is desirous to further reduce the stent""s compressed profile for loading onto smaller diameter catheters. Furthermore, the more the stent is handled the higher the likelihood of human error. Accordingly, there is a need in the art for a device that will reliably collapse a stent and allow it to be loaded into a smaller low profile delivery catheter.
There have been attempts at devising a tool for compressing a stent, most of which have been directed to the crimping of a balloon expandable stent onto a balloon delivery catheter. An example of such a tool embodies a series of plates having substantially flat and parallel surfaces that move in a rectilinear fashion with respect to each other. A stent carrying catheter is disposed between these surfaces, which surfaces crimp the stent onto the outside of the catheter by their relative motion and applied pressure. The plates have multiple degrees of freedom and may have force-indicating transducers to measure and indicate the force applied to the catheter during crimping of the stent.
Another stent loading tool design includes a tubular member housing a bladder. The tubular member and bladder are constructed to hold a stent that is to be crimped onto a balloon catheter assembly. Upon placement of the stent over the balloon portion of the catheter, a valve in the loading tool is activated to inflate the bladder. The bladder compresses the stent radially inward to a reduced diameter onto the balloon portion of the catheter to achieve a snug fit. In this way, the stent is crimped onto the distal end of a balloon catheter with a minimum of human handling.
Yet another stent crimping tool known in the art is constructed from a rigid, tubular body with a ball at one end connected to a plurality of long, thin strips passing through the tubular body. An uncrimped stent is placed over the plurality of long, thin strips, which hold the stent in an expanded state. The balloon portion of a catheter is inserted into the cylindrical space formed by the plurality of strips. When the user pulls the ball while holding the tubular body against the stent, the strips are slid from beneath the stent and the stent is transferred onto the balloon portion.
Still another conventional stent crimping tool appears similar to a hinged nutcracker. Specifically, the tool includes two hand operated levers hinged at one end and gripped in the palm of the hand at the opposite end. A cylindrical opening holding a crimping tube is provided through the mid-portion of the tool to receive therein a stent loaded onto a balloon catheter. The crimping operation is performed by the user squeezing the handle thereby pressing the crimping tube which in turn pinches the stent onto the balloon catheter.
While the prior art devices discussed above are suitable for and generally directed to crimping a typical balloon expandable stent onto a balloon catheter, they may not be suitable for collapsing and loading a self-expanding stent due to the tendency of such a stent to expand during the loading process. Additionally, because of this natural tendency to resist compression, prior art devices directed to crimping balloon expandable stents, when applied to self-expanding stents can suffer from problems such as non-uniform compressing forces, resulting in nonuniform collapsing. Consequently, what is needed is a device to collapse balloon expanded or self-expanding stents and load them into a low profile delivery catheter.
The present invention is directed to a collapsing tool that can repeatedly provide a uniform and tight collapse of a stent to ensure the low profile diameter of the stent in a compressed state for placement into a delivery catheter. More specifically, the present invention is directed to a collapsing machine that can compress a stent and properly load the same into a protective sleeve of a delivery catheter. The invention also provides a uniform compression force that is capable of maintaining a self-expanding stent in a compressed state therefore ensuring a minimized profile during the loading of the stent into a small diameter delivery catheter, thereby ensuring that the stent is properly loaded with minimum human intervention.
In a preferred embodiment, the present invention is directed to a machine for compressing a stent and loading it into a delivery catheter. The machine includes an elongate base plate having a top surface, a first end and a second end and a belt having a first end and a second end. A first and second sliding plate is slidably mounted to the elongate base plate top surface. A first belt mount may be affixed to the first sliding plate and a second belt mount may be affixed to the second end of the elongate base plate and each belt mount includes a bottom piece and a top piece for tightly securing the belt first end and the second end thereto. Additionally, a jaw block set is provided, the jaw block set includes a first jaw block and a second jaw block. The first jaw block may be stationarily mounted to the second sliding plate and a jaw block sliding plate having the second jaw block mounted thereon may also be slidably mounted to the second sliding plate at a position adjacent to the first jaw block. The jaw block sliding plate allows the second jaw block mounted thereon to be slidably translated back and forth in relation to the first jaw block.
The first and second jaw block define a top opening into the space in between the first and second jaw blocks. Once the belt is mounted onto the elongate base plate, the belt mid-portion is allowed to rest over the first and second jaw block and any lag occurring from the loosely mounted belt may be used to form a belt loop positioned within the jaw block setxe2x80x94in between the first and second jaw block for receiving a stent. Finally, the machine includes at least one actuating mechanism mounted on the elongate base plate top surface and the actuating mechanism is attached to the first end of the belt for providing a force unto the belt thereby pulling taut the loosely mounted belt. With a stent mounted within the belt loop, when the belt is pulled taut, the belt loop collapses thereby collapsing the stent placed therein.
The present collapsing machine invention is capable of imparting a radial pressure onto the stent work piece positioned within the belt loop by pulling taut the belt thereby compressing the belt loop thus collapsing the stent-support pin therebetween. The belt action evenly distributes the collapsing pressure to obtain a homogeneous and uniform collapse along the circumference of the stent.
In another preferred embodiment of the present invention, the machine further includes multiple jaw block sets. Two or more jaw block sets, each set having a first jaw block and a second jaw block mounted and configured in the same manner as the jaw block set discussed above may be mounted upon the elongate base plate. The number of jaw block sets which may be included in this configuration may be limited only by the desired length of the elongate base plate or by the desired length of the belt. This embodiment operates in much the same way as the first preferred embodiment and allows for the simultaneous collapsing and loading of multiple stent work pieces. It is contemplated that this embodiment will be particularly useful for purposes of mass production.
In yet another embodiment of the present invention, the machine further includes a second actuating mechanism. This second actuating mechanism provides for force to be applied to the belt at both of the belt ends thereby allowing for more pulling force to be applied during the stent collapsing procedure. This added component is especially useful when utilized in conjunction with the second preferred embodiment having multiple jaw block sets for simultaneously collapsing multiple stents because in such a situation, more pulling force may be desirable to adequately collapse all of the stents simultaneously.
During use, along with the collapsing machine as described above, a support pin may also be provided. The support pin includes a first section and a second section, the first section having a smaller diameter than the second section, and the first section and the second section is connected at a point defining a beveled step between the first section and the second section. The smaller first section of the support pin may be placed within an expanded stent to be collapsed and the entire stent-support pin assembly may then be inserted into the belt loop of the collapsing machine. Once inserted, the second jaw block may be positioned relative the first jaw block such that the belt loop top opening defined by the first and second jaw blocks is substantially pinched or closed off.
With the un-collapsed stent having the smaller first section of the support pin inserted therein positioned properly within the belt loop, the belt loop may be collapsed thereby collapsing the stent about smaller first section of the support pin. Finally, the support pin may be used to push the collapsed stent and load it into a low profile delivery catheter. This is accomplished by pushing the support pin until the beveled edge makes contact with and pushes upon the collapsed stent. Further pushing of the support pin will force the collapsed stent out of the collapsed belt loop and with a low profile delivery catheter in proper position, the collapsed stent may be pushed out of the belt loop and translated directly into the low profile delivery catheter thereby completing the loading process once the support pin is withdrawn from the now loaded stent.
The present invention collapsing machine is thus highly useful to cardiologists, for example. Such physicians are constantly concerned with proper deployment of the stent within the patient, especially where vessels become smaller and smaller, and it is desirable to have as small as possible a stent profile for loading into a very small stent delivery catheter. The present invention is further a time saver in that the stent collapsing procedure can be performed fairly efficiently and quickly. As such, the machine may further be used for production collapsing and loading of self-expanding stent designs. These and other advantages of the present invention will become apparent from the following detailed description thereof when taken in conjunction with the accompanying exemplary drawings.